Who was the first economist to have evolved the technique of indifference curve analysis?

In $1831$, electricity became viable for use in technology when ______ created the electric dynamo.

In $1831$, electricity became viable for use in technology when ______ created the electric dynamo.

The test for diagnosing HIV is:  

1. Pap Smear
2. ELISA
3. DND
4. Mantoux